The present subject matter relates to a mountable wing tip device, a blade tip assembly and a wind turbine arrangement.
In a commonly known wind turbine assembly, a rotor blade of a rotor component converts wind energy to low speed rotational energy. Such a rotor blade is connected to a generator positioned in a hub of the wind turbine assembly, wherein the hub is arranged in order to drive the generator while the rotor blade converts wind energy. Opposite to the end of the rotor blade arranged at the hub, the rotor blade comprises a free end which oscillates due to the mixture of the air flow from the pressure and suction side of the rotor blade.
Typically, a rotor blade is designed to be broader near a root portion and narrower towards a tip portion of the rotor blade wherein the tip portion comprises the free end of the rotor blade. As also known, for some of the prevalent rotor blade designs, the blade tip region is characterized by the region extending from the blade tip to about one-third of the length of the entire rotor blade. As would be appreciated by a person skilled in the art, the blade tip region contributes to the majority of the wind energy captured by the rotor blades. In some designs, nearly 70% of the wind energy is captured through the blade tip region.
Since a large extent of the wind energy is captured through the blade tip region (which in turn extends over a smaller portion of the entire rotor blade), any losses that may be occurring due to physical attributes of the blade tip region would tend to have a profound effect on the overall wind energy capture efficiency of the rotor blade. Thus, it is preferred to minimize losses occurring in the blade tip region.
One of the losses which are present in the blade tip region occurs primarily due to the axial direction which the airflow assumes as it flows over the rotor blade. In operation, the incoming winds are incident onto a leading edge region of the rotor blades. Normally, the airflow is such that it flows in a regular manner, from the leading edge region towards the sharper trailing edge region, along a direction which is perpendicular to the axis of the rotor blade. As one moves along the length of rotor blade towards the tip, owing to the sharp edge at the rotor blade tip, the airflow has a tendency to assume an axial flow, i.e. along a direction which is parallel to the axis of the rotor blade. Due to such non-regular airflow along the blade tip region, aerodynamic losses are introduced which in turn reduce the lift-to-drag efficiency of the rotor blade. In addition, the tip of the rotor blade may also produce tip vortices which in turn contribute to the reduced lift-to-drag ratio for the rotor blade.
To reduce the drag, the tip of the rotor blades of the modern wind turbines may be curved to form blade tips. As a result of the curved blade tip, the resulting drag produced due to the axial airflow can be reduced. However, despite the curved tip of the rotor blades, an aerodynamic short-circuit between a pressure side and a suction side of the rotor blade might occur. Further, as per conventional design, the blade tip can be a part or an extension of the rotor blade and is machined along with the rotor blade itself. Such designs however do not address the losses that occur due to the formation of the vortices.
The special design of the blades, i.e. the curved rotor blades, may also require additional consideration in transportation and assembling at the assembly site. As mentioned previously, any small perturbations in the structure of the rotor blades may have substantial effect on the efficiency of the rotor blades. It may therefore be understood that the design of the rotor blades has to be precise and free from defects. Since the shape and design of such blades are required to be precise, any damage occurring due to wear and tear either during operation or during transportation will also have effect on the efficiency of the blade.
In cases where the blade tip is part of the rotor blades, it is very likely that the blade tips may get damaged during transportation. Also, if the blade tips suffer damage in the course of their operation, or due to natural occurrences such as lightening, the entire rotor blade has to be replaced. This further is likely to increase the operational costs associated with the wind turbine.
In addition, it may be inconvenient and time-consuming to perform any checks on the blade tips, once the wind turbine is operational. Further, since the blade tips typically extend either towards the suction side or the pressure side of the rotor blade, this may cause imbalance when the wind turbine is in operation, thereby causing vibrations in the wind turbine.